Fuel cell stack systems are used as a power source for electric vehicles, stationary power supplies, and other applications. One known fuel cell stack system is the proton exchange membrane (PEM) fuel cell stack system that includes a membrane electrode assembly (MEA) comprising a thin, solid polymer membrane-electrolyte having an anode on one face and a cathode on the opposite face. The MEA is sandwiched between a pair of electrically conductive contact elements which serve as current collectors for the anode and cathode, which may contain appropriate channels and openings therein for distributing the fuel cell stack system's gaseous reactants (i.e., H2 and O2 or air) over the surfaces of the respective anode and cathode.
PEM fuel cells comprise a plurality of the MEAs stacked together in electrical series while being separated by an impermeable, electrically conductive contact element known as a bipolar plate or current collector. The fuel cell stack systems are operated in a manner that maintains the MEAs in a humidified state. The level of humidity of the MEAs affects the performance of the fuel cell stack system. Additionally, if an MEA is operated too dry, the useful life of the MEA can be reduced. To avoid drying out the MEAs, the typical fuel cell stack systems are operated with the MEA at a desired humidity level, wherein liquid water is formed in the fuel cell during the production of electricity. Additionally, the cathode and anode reactant gases being supplied to the fuel cell stack system are also humidified to prevent the drying of the MEAs in the locations proximate the inlets for the reactant gases. Traditionally, a water vapor transfer (WVT) unit is utilized to humidify the cathode reactant gas prior to entering into the fuel cell. See, for example, U.S. Pat. No. 7,138,197 by Forte et al., incorporated herein by referenced in its entirety, a method of operating a fuel cell stack system incorporating a WVT unit.
Typical WVT units are located away from a cathode outlet and a cathode inlet of the fuel cell stack of the fuel cell stack system. Other fuel cell stack assemblies include WVT units incorporated into the end unit and adjacent the fuel cell stack. In these fuel cell stack systems, an end plate of the fuel cell stack is formed from a metal to provide support to the fuel cell stack. However, because the end plate is formed from a metal, the weight and thermal conductivity of the end plate is increased, thereby increasing the overall weight of the fuel cell stack system and increasing a warm up time of the fuel cell stack system due to heat losses.
It would be desirable to produce a water vapor transfer unit assembly adapted to provide support to an end plate of the fuel cell stack system to facilitate an integration of the water vapor transfer unit assembly with an end unit of a fuel cell stack system while minimizing the weight and thermal conductivity of the fuel cell stack system.